(a) Field of the Invention
The present invention relates generally to an exercise apparatus, and more particularly to a sit-up exercise apparatus which is safe, smooth and comfortable to operate.
(b) Description of the Prior Art
A prior sit-up exercise apparatus 10 is shown in FIG. 1. The prior apparatus essentially comprises two curved bars 11 arranged in a parallel relation at opposite ends of an inverted-U shaped stem 12. The stem 12 has a middle section with a head rest 13 disposed thereon and a curved stem 14 extending therefrom. The end of the curved stem 14 is connected to a horizontally disposed hand grip 15. Each of the curved bars 11 has a pad 16 substantially vertically provided thereon at a suitable position. With reference to FIG. 2 which illustrates operation of the prior apparatus 10, a user lies flat between the curved bars 11 with his/her head resting on the head rest 13 and both hands gripping the ends of the hand grip 15. When the user pushes the hand grip 15 forwardly, the curved bars 11, by means of their curved sections 111 as the pivots, will rotarily displace forwardly so that the upper trunk of the user rises. However, it has been found that users of this type of sit-up exercise apparatus are quite uncomfortable and scared when using it. This is because when the user pushes the hand grip 15 forcefully forward so as to lift the trunk, the pivots of the apparatus, i.e., the curved sections 111 of the curved bars 11, will be subjected to the reverse action of the forward force to displace rearwardly, so that a pivot A displaces forwardly to near a point B closer to the end of the curved section 111, and when the apparatus 10 displaces rearwardly and then forwardly again with the push of the user's hands on the hand grip 15, the pivot A will shift to A', and the pivot A' will displace forwardly to the point B'. As a result, with every push of the hand grip 15, the pivot of the apparatus shifts forwardly, affecting the user's operation of the apparatus. Worse still, if the user exerts an excessive force on the hand grip 15, the whole apparatus might overturn and hurt the user.
There is another type of sit-up apparatus designed to overcome the drawbacks with the above-described apparatus. With reference to FIG. 3, a sit-up exercise apparatus 20 essentially comprises a U-shaped bottom bar 21 with two slightly curved ends, a head rest 22 fixedly disposed at a straight section 211 of the bottom bar 21, an inverted-U shaped handle bar 23 having its ends fixed secured to two side arms 212 of the bottom bar 21, and a support seat 24 is pivotally mounted at each curved end of the bottom bar 21. In use, the user lies flat between the two side arms 212 of the bottom bar 21 with his/her head resting on the head rest 22. When the user grips the handle bar 23 and pushes forwardly, the bottom bar 21 will rotarily displace upwardly with the support seats 24 as the pivots, lifting the user's trunk. At this time, as the apparatus 20 is provided with two support seats 24 as the pivots, undue displacement of the pivots when the user exerts a force on the handle bar 23 to bring the bottom bar 21 to rotarily displace may be prevented. In other words, the entire apparatus 20 will not displace rearwardly with the movement of the user. However, such a design engenders another problem. With reference to FIG. 4, when the user exerts a force on the handle bar 23 to lift his/her trunk up, the apparatus 20 utilizes the support seats 24 as its pivots so that the bottom bar 21 displaces through an angle with the handle bar 23, so that the user's body is supported by his/her buttocks and his/her upper trunk lifted by the bottom bar 21. However, as can be seen from FIG. 4, a distance C from the support seats 24 to the head rest 22 and a distance D from the user's buttocks to the head rest 22 is different (i.e., the radius of rotation is not the same). Therefore, when the bottom bar 21 displaces upwardly and the user's upper trunk is lifted, the user's head will move away from the head rest 22 so that only a part thereof or the neck touches the head rest 22, which is very uncomfortable and will thus affect the exercising effects.